A number of forms of ink jet printer have been used to apply ink compositions to a wide range of substrates. In many cases the ink is put up in the form of a solution or suspension in an organic solvent, notably MEK. The use of MEK provides an ink which is highly suitable for use in ink jet printers, since it gives an ink which can readily be jetted, which is aggressive to many plastic substrates so that the printed image adheres firmly to the substrate, and which dries rapidly so that the printed image resists smudging or smearing allowing the printed substrate to be handled almost immediately after printing. Furthermore, MEK readily dissolves most of the dyestuffs and other components used in ink compositions, giving the printer the freedom to use a wide range of ink compositions.
Despite the many technical advantages in the use of MEK and similar solvents, major problems arise in that such solvents are often toxic or present health hazards and are becoming less and less acceptable from an environmental standpoint. Thus, MEK is flammable and presents a health hazard, notably when vapours are inhaled or fluid contacts the skin, and it would be desirable to use a solvent or carrier medium for the ink which is physiologically acceptable, notably so as to allow the ink to be applied directly to a foodstuff or to packaging closely associated with a foodstuff.
It has therefore been proposed to use lower alkanols or water as the solvent or carrier medium for the ink. Whilst such solvent or carrier media reduce or avoid the physiological problems associated with the use of MEK, ink formulations using such a solvent or carrier dry slowly and spread upon contact with non-porous surfaces, notably many of the clay filled glossy surfaced papers currently used in the packaging industry, so that the printed image smears and loses its sharp definition. Furthermore, since many of the dyestuffs or other components required for the ink compositions are often insoluble or only slightly soluble in water or alkanols, the use of such solvent or carrier media limits the range of ink formulations the printer can use.
We have now found that the use of acetone as the major constituent of the carrier medium reduces the above problems and provides an edible ink which can be applied directly to a foodstuff or to packaging in immediate contact with the foodstuff.